Semiconductor substrate processing, such as, for example, for manufacturing integrated circuits, often includes processing the substrates in a vacuum chamber. The pressure within the vacuum chamber may be adjusted (e.g., below or above atmosphere) to facilitate processing of the semiconductor substrate.
In order to maintain the vacuum chamber at a desired vacuum pressure, while transferring substrates in and out of the chamber, a load lock is often employed. For example, one or more substrates may be placed in the load lock under atmospheric conditions. The load lock may then be sealed and the pressure within the load lock may be adjusted (i.e., pumped down) to approximate the pressure in the vacuum chamber. The one or more substrates may then be retrieved from the load lock and subjected to one or more processing steps within the vacuum chamber. Moving substrates between the load lock and one or more processing platens within the vacuum chamber is often performed with the use of robotic arms, such as, for example, a selective compliance assembly robot arm (SCARA). Where multiple substrates are transferred to the load lock together they may be supported by a lift, which holds the substrates in a stacked arrangement with a gap maintained between adjacent substrates. The robot arm may be inserted into the gap between adjacent substrates to engage an individual substrate for transfer.
The size and weight of semiconductor substrates continues to increase. As will be appreciated, the robot arms used to transport these larger substrates must be able to support these heavier substrates. At the same time, size constraints within vacuum chambers may require robot arms to support these substrates over increasingly longer distances. Due to the increased weight of the substrates and longer reach requirements of the robot arms, the robot arms may droop. In some cases, this droop may be substantial and may result in contact between the robot arm and adjacent substrates as the robot arm is being inserted into the gap between substrates.
One solution is to increase the gap between substrates in the substrate lift. As will be appreciated, however, such a solution would require that the size of the load lock be increased. But increases in load lock sizes would result in longer pumping and venting times, which would undesirably increase the time for transferring substrates between vacuum and atmosphere environments, with a corresponding negative effect on throughput.